1. Field of the Invention
This invention relates to a multi-piece solid golf ball having durability against repetitive hits, an increased distance of travel, controllability and scuff resistance.
2. Prior Art
From the past, the spin control of a ball when hit with a short iron is important for low-handicap players. It has been an outstanding task in the golf ball development work to improve the spin control of a two-piece golf ball having a cover formed of a hard ionomer resin without adversely affecting the flight distance capability inherent to the ball.
For example, U.S. Pat. No. 4,431,193 discloses a three-piece solid golf ball comprising a core, a cover inner layer formed of a hard ionomer resin, and a cover outer layer formed of a soft ionomer resin. It is intended to improve the spin rates of the ball both when hit with a driver and a short iron. This ball, however, is inferior in scuff resistance and flight distance to two-piece solid golf balls. Improvements in these respects are desired.
JP-A 343718/1994 discloses a three-piece solid golf ball comprising a cover inner layer formed of a high modulus ionomer resin having a relatively high acid content and a cover outer layer formed of a low modulus ionomer resin having a relatively low acid content or a thermoplastic elastomer exclusive of an ionomer resin. However, when the cover outer layer is formed of a thermoplastic elastomer resin, the ball can become less repulsive and less durable on account of the poor bond between the thermoplastic elastomer for the outer layer and the ionomer resin for the inner layer.
An object of the present invention is to provide a multi-piece solid golf ball having superior flight distance performance to prior art two-piece solid golf balls, durability against repetitive hits, and improved playability including control, spin and scuff resistance on short iron shots.
The invention provides a multi-piece solid golf ball comprising a solid core and a cover consisting of inner and outer layers. The cover inner layer is composed mainly of an ionomer resin containing at least 15% by weight of an xcex1,xcex2-unsaturated carboxylic acid. The cover outer layer is composed mainly of a thermoplastic elastomer exclusive of an ionomer resin. In one aspect, an adhesive layer composed mainly of a thermoplastic resin is interposed between the cover inner and outer layers. In another aspect, an adhesive composed mainly of a thermoplastic resin is blended in the inner and/or outer layer cover stock.
Since the adhesive or adhesive layer establishes a firm bond between the cover inner layer and the cover outer layer, the ball of the invention is significantly improved in durability against repetitive hits. When hit with a driver, the ball can travel a longer distance by virtue of a low spin rate. On approach shots with a short iron or the like, the ball is well controllable by virtue of an increased spin rate and is fully resistant to scuffing.